Recently, accompanied by development of communication networks and a rapid increase in popularity of the internet, an increasing number of offices and households are building LANs (Local Area Networks). Further, there is a remarkable increase in need for so-called wireless LANs. This is because (I) digital wireless communication technology has advanced, and (II) the wireless LAN allows a user to wirelessly establish a LAN, so that the user is freed from burdens due to wiring. Further, since the wireless LAN allows a mobile terminal, such as a laptop computer, to be used in a mobile environment, a significant increase in a popularity of the wireless LAN is expected in the future.
As a representative technology for such a wireless LAN, there is IEEE802.11, which is already standardized by IEEE (Institute of Electrical and Electronics Engineers). IEEE802.11 prescribes from a physical layer to a MAC (Media Access Control) Layer in an OSI (Open Systems Interconnection) model, the MAC layer being a lower layer of a data link. Further, IEEE 802.11 can be replaced by Ethernet® which is a wired LAN transmission channel. Further, since IEEE 802.11 is a wireless technology, it can provide a roaming function as an additional function.
Today, new terrestrial digital broadcasting is in the process of replacing terrestrial analog broadcasting, which is currently viewed/listened to throughout Japan. This terrestrial digital broadcasting, which was launched in 2003 in three major metropolitan areas of Japan (i.e., Kanto, Kinki, and Tokai areas), is due to spread through the rest of Japan by 2006. Along with this, the current terrestrial analog broadcasting will fall into disuse by 2011.
ISDB (Integrated Services Digital Broadcasting) is a format for integrated digital broadcasting of the next generation. This format allows various kinds of information, such as images, sound, and data, to be handled in the form of digital data. As specific examples of services adopting ISDB, digital television broadcasting, digital voice broadcasting, facsimile broadcasting, multimedia broadcasting, or the like are under development. Under ISDB, it is planned that a satellite broadcast wave, a terrestrial broadcast wave, or a wired transmission channel (e.g., coaxial cable, or optical fiber) will be used as a transmission channel (extracted and translated from Nikkei BP digital unabridged dictionary; published by Nikkei Business Publication inc.).
ISDB-T(Terrestrial), which is an ISDB technical standard for terrestrial digital broadcasting, adopts a modulation method called OFDM (Orthogonal Frequency Division Multiplexing) in which many carriers are used. With the use of this method, it becomes possible to restrain ghosting, which occurs due to multiple-paths caused by, for example, a reflection of a signal from a building. Further, remarkably many signal formats are allowed under ISDB-T. This is because ISDB-T prescribes a plurality of: (I) transmission modes, each of which prescribes an interval of the carriers; (II) modulation methods, each of which is defined on a carrier-by-carrier basis; and (III) guard intervals in a direction of the time axis, each of which is provided for every effective symbol length. Amongst the allowable formats, an optimum format is selected in accordance with a service type, such as a service in which a fixed-reception is carried out, or a service in which a mobile-reception is carried out.
Further, under the ISDB-T, a single transmission channel (communication channel)(Band of approximately 5.6 MHz) is divided into 13 segments (1 segment=approx. 430 kHz). Each of the segments serves as a unit at which a modulation method is varied. This allows a broadcasting station to desirably determine a signal configuration in one channel; e.g., a signal configuration including voice broadcasting, high-vision broadcasting, standard fixed broadcasting, and mobile broadcasting.
ISDB-T adopts an interleave in a direction of the time axis, and an electric wave used is suitable for data-transmission with respect to a mobile device. On this account, it is one of the distinct characteristics of ISDB-T that stable reception is possible even with a mobile receiver such as an in-vehicle television, or a portable terminal such as a PDA (Personal Digital Assistant) or mobile phone. A service assuming such a mobile reception will cause a great deal of expectations in the future.
Incidentally, in such a wireless communication system, there has been a wireless AV system including: (I) one center device provided with various tuners and/or external input terminals or the like; and (II) a plurality of terminal devices, for (i) wirelessly receiving content data from the center device, and (ii) carrying out a display output and/or an audio output. In this case, a user can control the center device via wireless communication, by entering an instruction or the like for remotely operating the terminal device.
More specifically, in such a wireless AV system, when the user uses a remote operation device (hereinafter referred to as remote controller) for outputting, to the terminal device, a remote-controller signal from the remote controller, the terminal device encodes the remote-controller signal thus received, and then transmits the encoded-data to the center device. The center device decodes the encoded-data thus received, so as to obtain the remote-controller signal. Then, based on the remote-controller signal thus obtained, a predetermined control is carried out.
Here, if the remote-controller signal which is obtained by the center device contains, as it is, the remote-controller signal received by the terminal device, an LED (Light Emitting Diode) device or the like is used for, for example, transmitting the remote-controller signal in the form of an infrared signal. This infrared signal is received by an infrared receiving section of an external device existing in a vicinity of the center device, so that the remote operation carried out by the user with respect to the terminal device is carried out with respect to the external device. In the present specification, such a remote operation is hereinafter referred to as “remote-control-through”.
Patent document 1 discloses an audiovisual distribution system having the remote-control-through function. This audiovisual distribution device includes: (I) an audiovisual transmitting device for wirelessly transmitting audiovisual content; (II) an audiovisual receiving device for (i) receiving the audiovisual content thus transmitted, and (ii) causing an image-receiving device, such as a connected television or the like, to display the audiovisual content.
Firstly, the user uses an AV-device-selecting button, so as to select a desired AV device through the audiovisual receiving device. Then, by using the remote controller, the user enters a reproduction instruction or the like. Next, the audiovisual transmitting device analyzes AV-device-selection information in a telegraphic message wirelessly transmitted from the audiovisual receiving device, so as to select the AV device. Next, the audiovisual transmitting device causes its infrared emitting section to emit light, based on infrared data having been wirelessly received from the audiovisual receiving device, so as to transmit the infrared data to the AV device. Then, the audiovisual receiving device receives the audiovisual content transmitted from the selected AV device, and then displays the audiovisual content on the image-receiving device such as a television.
In this way, it is possible to (I) select the desired AV device from the plurality of the AV devices, and (II) reproduce, on a TV which is not directly connected to the AV device (e.g., a TV in a remote area such as an adjacent room), the audiovisual content transmitted from the selected AV device.
Further, Patent document 2 discloses a system in which a user-terminal having a remote-controller function is connected with a server device, in a communication-enabled manner, via a network, the system including means for transmitting, upon a request from the user, specified remote-controller information to the user-terminal.
Here, Patent document 1 is Japanese Unexamined Patent Publication No. 134502/2000 (Tokukai 2000-134502; published on May 12, 2000).
Here, Patent document 2 is Japanese Unexamined Patent Publication No. 291073/2002 (Tokukai 2002-291073; published on Oct. 4, 2002).
In the foregoing wireless AV system, the following case is possible. Namely, a plurality of users may remotely operate a plurality of terminal devices. Further, a plurality of external devices may be connected to the center device. In these cases, the center device may not be able to identify which external device the instruction of the remote operation entered by the user is directed to. This problem occurs likewise in the above-mentioned remote-control-through.
In view of the foregoing problem, in Patent document 1, the user uses the AV-device-selecting button for selecting the desirable AV device using the audiovisual receiving device (terminal device). Then, the audiovisual receiving device transmits, to the audiovisual transmitting device (center device), the AV-device-selection information along with the infrared data, so that the audiovisual transmitting device can analyze the AV-device-selection information and select an operation-targeted AV device.
However, there are various kinds of the external devices that can be connected to the center device. For example, the external device can be: (I) an apparatus for recording and reproducing an image and a sound, such as a VTR (Video Tape Recorder), a DVD (Digital Versatile Disk) recorder, and a HDD (Hard Disk Drive) recorder; (II) an apparatus for receiving various broadcast signals such as an STB (Set Top Box) and a tuner; and (III) an apparatus for creating image and sound signals, such as a video camera. Accordingly, it is necessary to increase the number of buttons, corresponding to the variety of the external devices.
Further, if (i) AV-device-selecting buttons of the terminal device are assigned on a basis of a connection configuration of the AV devices with respect to the center device, and (ii) the configuration of the connections between the center device and the AV devices changes, it is not possible to know which one of the AV-device-selecting buttons allows the remote operation of which one of the AV devices.
The present invention is made in view of the foregoing problem, and it is an object of the present invention to provide a terminal device, a center device, a communication system or the like, each of which allows remote operation of a desired external device, through a plurality of terminal devices, even if various external devices are connected to the center device
Further, it is also an object of the present invention to provide a wireless AV system including a plurality of AV devices, the system such that data, for use in identifying an external device that is the target of an operation, can be transmitted/received along with remote-control data, when the remote-controller data is wirelessly transmitted/received between devices, upon operation of a remote-controller.